In the field of vehicle manufacture, the replacement of certain metal components by ceramic components is becoming increasingly important and the non-oxidic, ceramic materials of silicon nitride and silicon carbide have, for example, proven successful. The particular fields of application for ceramic components are gas turbines and exhaust gas turbocharger rotors for diesel engines and spark-ignition engines.
In a runner, which consists of both ceramic and non-ceramic components--a ceramic rotor with an integrated ceramic shaft and a non-ceramic compressor impeller, for example--the type of connection between the components in the different materials (shaft/compressor impeller) is critical. This connection must be able to resist high thermal and mechanical loads when the ceramic rotor is put into rotation by the exhaust gas energy from the engine, rotational speeds of more than 140,000 rpm and temperatures of more than 1,000.degree. C. being reached; the rotation is transferred to the compressor impeller, which forces the air under increased pressure into the combustion chamber.
Known jointing techniques for ceramic/metal connections, such as brazing, bonding or shrinking, which have already proven themselves as permanent connections between rotor blades and the rotor disk or between the rotor disk and the rotor shaft (see DE-C No. 28 22 627 and J. E. Siebels in "Fortschrittsberichte der Deutschen Keramischen Gesellschaft", Volume 2 (1986/7), No. 1, pp 277-293) cannot be used for the application envisaged because it must be possible to release the connection between the shaft and the compressor impeller to facilitate repair.
Releasable screw threads, however, cannot be used on ceramic components because of the brittleness of the material or, alternatively, they can only be used by means of additional metallizing, which is not only expensive but also, because of the radial space requirement of the metal layer, it reduces its strength and forces a reduction in the diameter of the ceramic shaft.
Accordingly, one or more of the following objects will be achieved by the practice of the invention.
It is an object of this invention to provide a runner with mechanical coupling which is comprised of both ceramic and non-ceramic components.
Another object of the invention is to provide a runner, which consists of a radial turbine ceramic rotor with an integrated ceramic shaft and a non-ceramic compressor impeller, a thermally and mechanically loadable connection, which can be released if required.
These and other objects will readily become apparent to those skilled in the art in light of the teachings herein set forth.